Revaporization of liquefied gases



March 21, 1961 w. w. BODLE 2,975,607

REVAPORIZATION 0F LIQUEFIED GASES Filed June 11, 1958 3 Sheets-Sheet 1E- I L 55 FUEL T0 V ii GENERATORS Z j LEA/(AGE ETC. E

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A TTOP/VE Y March 21, 1961 w. w. BODLE 2,975,607

REVAPORIZATION OF LIQUEFIED GASES Filed June 11, 1958 5 Sheets-Sheet 272 b \J F 1'5. 2

84 72 m fl L V V INVENTOR.

PM. a m/mm w 664/! BY am I WLUM a WM ATTOPNEY March 21, 1961 w. w. BODLEREVAPORIZATION OF LIQUEFIED GASES 3 Sheets-Sheet 3 Filed June 11, 1958INVENTOR. 0M Ha f/ WM/m/n BY A TI'OENE-X United States PatentREVAPORIZATION or LIQUEFIED GASES William W. Bodle, Deerfield, Ill.,assignor, by mesne assignxnents, to Conch International Methane Limited,

Nassau, Bahamas, a corporation of the Bahamas Filed June 11, 1958, Ser.No. 741,336

9 Claims. (CI. 62-52) This invention relates generally to improvementsin the art of preparing a liquefied natural gas for use as a fuel, andmore particularly, but not by Way of limitation,

to an improved method of revaporizing a liquefied gas. Natural gas isavailable in certain localities in amounts considerably greater thandemanded in those localities, While in other localities a markeddeficiency exists in the amount of natural gas available for use. Forthe most part, where the source of plentiful supply is joined by landwith the areas where a deficiency exists, transfer can be economicallyachieved by means of pipeline and the like wherein transfer is effectedwhile the gas remains in the gaseous state. Where the area having adeficiency is somewhat isolated, or where the source of supply and thearea where a deficiency exists are separated by a large body of water,transfer by pipeline becomes impractical. In the latter instance, anindustry is in the stage of development wherein the natural gas isliquefied at the source of supply and transported in the liquefied stateto the area wherein a deficiency exists, and the liquefied natural gasis revaporized at that point for use. By conversion of the natural gasfrom the gaseous state to the liquefied state, it becomes possible tocarry as much as 600 times more gas in a given space, thereby makingtransportation practical.

Transportation is effected with the liquefied natural gas housed inlarge insulated containers at about atmos pheric pressure or slightlyabove, and vw'th the natural gas at a temperature as low as -258 F. Thelatter temperature represents the boiling point temperature for methaneat atmospheric pressure. However, since natural gas has small amounts ofheavier and higher boiling hydrocarbons, such as ethane, propane, butaneand the like, the liquefied gas will be characterized by a some- Whathigher boiling temperature, usually ranging from 240 to 258 F.,depending upon the amount of the heavier hydrocarbons.

At the point of use, the liquefied natural gas must, in all cases, bevaporized before being used as a fuel. However, a natural gas containinga substantial portion of methane will, in many countries, have a heatingvalue far above the specifications for a gas which may be used inexisting equipment, and variation or adjustment might also be requiredin its specific gravity. In these countries it is therefore requiredthat the liquefied gas not only be revaporised, but also reformed to alower heating value and to adjust the specific gravity. Such reformingoperations may be carried out in the locality where the liquefied gas isrevaporized. In many instances, the actual point of use of the gas maybe located a substantial distance from the point where the liquefied gasbecomes available, as when the point of use is inland and the liquefiedgas is transported by ship. In such instances, it is desirable that theliquefied gas be revaporized and pressurized at the point where theliquefied gas is made available, but that the gas be reformed nearer thepoint of use. This is particularly desirable where the reformed2,975,667 Patented Mar. 21, 1961 gas will have a volume substantiallygreater than that of the revaporized natural gas.

As previously noted, a liquefied natural gas at about atmosphericpressure will have a temperature of about 240 to 258 F. Such a liquefiedgas may be revapon'zed in accordance with present vaporization practicesby passing the same in heat exchange relation with a readily availableheat source, such as air or sea water. However, when such a coldmaterial is passed in heat exchange relation with water, the tubes ofthe heat exchanger will be at a temperature far below the freezingtemperature of the water. The tubes will rapidly become coated with iceto reduce the heat transfer efiiciency, either resulting in completestoppage of water flow through the heat exchanger, or requiring an overdesign of the heat exchanger to accommodate the inherent ice formation.When using air instead of water, hydrates will form and precipitate outof the air onto the tubes of the heat exchanger, resulting insubstantially the same problem as when using water.

The present invention contemplates a novel method of revaporizing aliquefied gas by use of a heat transfer medium passing in heat exchangerelationship with a readily available and cheap heat source, such as seawater or air, and, alternately, the liquefied gas. The primaryrequirement of the heat transfer medium is that its freezing temperaturebe below the temperature of the liquefied gas, such that no solids willform on the tubes of the heat exchanger through which the liquefied gasand the heat transfer medium are passed. Also, the heat transfer mediumis used in such a quantity that the temperature thereof when passing inheat exchange relation with the heat source is higher than the freezingtemperature of any component of the heat source, but [lower than thetemperature of the heat source. In a preferred embodiment of thisinvention, the heat transfer medium is a liquid which is vaporized byheat exchange with the heat source and condensed by heat exchange withthe liquefied gas, such that the latent heat of the heat transfer mediumwill be the principal factor in vaporizing the liquefied gas.

This invention further contemplates reducing the pressure of thevaporized heat transfer medium prior to passage thereof in heat exchangerelation with the liquefied gas to obtain work from the heat transfermedium. After the heat transfer medium is condensed by the liquefiedgas, it is again increased in pressure before being revaporized by theheat source. The difference in the work obtained by a decrease in thepressure of the vapor, and the work required to increase the pressure ofthe condensed heat transfer medium, may be utilized as an auxiliarypower supply in a system involving practice of the invention.

An important object of this invention is to facilitate the preparationof a liquefied natural gas for use as a fuel.

Another object of this invention is to efficiently and economicallyrevaporize a liquefied gas either for use as a fuel or fortransportation through a pipeline or the like to a reforming plant.

Another object of this invention is to utilize heat from a readilyavailable and cheap heat source to revaporize a liquefied gas having aboiling temperature far below the freezing temperature of some componentof the heat source, without the formation of solids on the tubes of theheat exchanger used for vaporizing the liquefied gas. A further objectof this invention is to utilize a readily available heat transfer mediumfor transferring the heat from a cheap heat source to a liquefied gasfor revapon'zing the liquefied gas.

Another object of this invention is to provide a method evident from thefollowing detailed description, when read in conjunction with theaccompanying drawings which illustrate this invention.

In the drawings:

Figure lis a flow diagram illustrating a practice of this invention.

Figure 2 is a flow diagram illustrating a modified practice of thisinvention.

Figure 3 is a modification of Fig. 2 illustrating still anot-herpractice of this invention.

Figure 4 is a flow diagram of a typical commercial installationillustrating a practice of the present invention.

Referring to the drawings in detail, and particularly Fig. 1, referencecharacter 6 designates a line for feeding liquefied natural gas to astationary, insulated storage tank 8. The line 6 extends from acontainer (not shown) used for transporting the liquefied natural gaswhich, as previously noted, will ordinarily be aboard a ship. Theliquefied natural gas in the tank 8 will normally be at aboutatmospheric pressure, or slightly above, and have a temperature of about240 to -258 F.

Although a portion of the liquefied natural gas in the tank 8 will boiloff as a vapor during storage, as will be hereinafter more fullydescribed, the major portion of the liquefied natural gas in the tank 8is fed through a line 10 to a suitable pump 12. The pump 12 increasesthe pressure of the liquefied natural gas to the pressure at which it isdesired to either immediately reform the gas, used the vaporized gas asfuel, or transport the gas through a pipe line to a distant reformingplant, as previously indicated. The pressure of the liquefied naturalgas discharging from the pump 12 may therefore be anywhere from slightlyabove atmospheric pressure to about 600 pounds per square inch, but isusually from about 50 to about 200 pounds per square inch.

The liquefied natural gas discharged through the line 14 from the pump12 is directed through a vaporizer 16 where the liquefied gas isrevaporized by a heat transfer medium circulated in a closed cycle, aswill be described in detail below. The revaporized natural gas is thendirected through a line 18 to a separator 20 for removing any condensatewhich may exist after passage of the stream through the vaporizer 16.The condensate removed in the separator 20 is returned through a line 22to the intake of the pump 12 where it may be re-circulated to thevaporizer 16. The overhead from the separator 20 consists solely ofrevaporized natural gas and is discharged through a line 24 to either afuel gathering system or a reforming plant, as previously indicated.

The vapor boil-off or over head from the storage tank 3 is directedthrough a line 26, partially to a compressor 28 and partially to he usedas a fuel in an engine 34} operating the compressor 28. The vaporpassing through the compressor 28 is increased in pressure to thepressure of the liquefied natural gas in the line 14 and is dischargedthrough a line 32 to be combined with the vapor in the line 24discharging from the separator 20. It will also be noted that a by-passline 34 may be run from the line 24 back to the engine 30 for supplyingadditional fuel if desired.

The heat transfer medium previously mentioned is circulated from-thevaporizer 16 through a line 36 to another vaporizer 38, and then througha line 44} back to the vaporizer 16. This heat transfer medium, 'as willbe described, provides a transfer of heat from a readily available andcheap heat source circulated through the vaporizer 38 izationprogresses.

to the natural gas circulated through the vaporizer 16. The heat sourcefor the vaporizer 38 must have a temperature above the boilingtemperature of the liquefied gas being vaporized and may take anydesired form, but is preferably a material which is readily availableand cheap, such as sea water or air. Sea water is the preferred heatsource. The water is directed through a line 42 from a source of supply(not shown) and is pumped by a suitable pump 44 through a line 46 to thevaporizer 38. In the vaporizer 38, the water is passed in heat exchangerelation with the heat transfer medium to supply an amount of heat tothe heat transfer medium at least equal to the amount of heat dissipatedfrom the heat transfer medium in the vaporizer 16, as previouslyindicated. After passage through the vaporizer 38, the water isdischarged through a line 48 to a suitable disposal point.

The heat transfer medium may be any fluid having a freezing point belowthe boiling temperature of the liquetied natural gas, to prevent thedeposition of solids in the vaporizer 16, and which, in passage throughthe vaporizer 38, has a temperature above the freezing temperature ofthe heat source but below the actual temperature of the heat source. Theheat transfer medium may therefore be in liquid form during itscirculation through both of the vaporizers 16 and 38 to provide atransfer of sensible heat alternately to and from the heat transfermedium. When the heat transfer medium is in continuous liquid form,however, a large volume of heat transfer medium must be circulatedthrough the system, since the temperature reduction thereof by passagethrough the vaporizer 16 is necessarily limited to such an extent as toretain the temperature of the heat transfer medium returning to thevaporizer 38 at a temperature higher than the freezing temperature ofthe heat source. It is therefore preferred that a heat transfer mediumbe used which goes through phase changes during circulation through thevaporizers 16 and 38, with a resulting transfer of latent heat.

The preferred heat transfer medium has a moderate vapor pressure at atemperature between the actual temperature of the heat source and thefreezing temperature of the heat source to provide a vaporization of theheat transfer medium during passage thereof through the vaporizer 38.Also, the transfer medium, in order to have a phase change, must beliquefiable at a temperature above boiling temperature of the liquefiednatural gas, such that the heat transfer medium will be condensed duringpassage through vaporizer 16. As before, the freezing temperature of theheat transfer medium must still be below the boiling temperature of theliquefied natural gas. It should also be noted that when the liquefiedgas is a pure, or substantially pure, compound, it will boil at aconstant temperature and absorb latent heat at that temperature. If theliquefied gas is a mixture of compounds, it will, in most cases, boilover a temperature range, the temperature increasing as Vapor- In thiscase, it will be desirable to make the heat transfer medium av mixtureof compounds .of such composition that the heat transfer medium willcondense over a range of temperatures some what above the vaporizingtemperature range of the liquefied gas, thereby making it possible torecover all of the latent heat in the liquefied gas by condensing theheat transfer medium.

Although some commercial refrigerants may be used as heat transfermediums in the practice of this invention, propane and ethane andpreferred heat transfer mediums, particularly in View of the fact thatthey are normally present in at least minor amounts in natural gas andtherefore readily available. It should be noted in passing that neithermethane nor butane will Work as a heat transfer medium in the practiceof this embodh ment of the invention, since they do not possess therequired characteristics. r

By using a heat transfer medium which goes through phase changes incirculating through the Vaporizers 16 and 38, two important advantagesare obtained. Firstly, the required quantity of heat transfer medium isreduced to a minimum, since mostly (or only) latent heat changes in theheat transfer medium are utilized, rather than only sensible heatchanges. Secondly, the heat transfer medium may be circulated throughthe Vaporizers 16 and 38 by gravity. By locating the vaporizer 16physically above the vaporizer 38, the heat transfer medium condensingin the vaporizer 16 will flow by gravity into the lower vaporizer 38. Onthe other hand, the heat transfer medium being vaporized in thevaporizer 38 will rise through the line 40 into the vaporizer 16,thereby reducing the energy required to vaporize the liquefied naturalgas.

In a commercial system, a portion of the revaporized natural gasdischarging through the line 24 will be diverted through a line 50'forsuch purposes as heat for buildings used in conjunction with thepractice of the invention, and as a fuel for generators and the like, asindicated by the blocks in the lower portion of the flow diagram. Also,a block has been included to indicate that a certain portion of thenatural gas is inherently lost by venting and leakage.

A modified system is illustrated in Fig. 2, wherein reference character52 designates a heat exchanger functioning as a boiler, and referencecharacter 54- designates another heat exchanger functioning as acondenser for a heat transfer medium. In this embodiment, the heatsource is again preferably sea water which is circulated through a line56, the tubes of the heat exchanger 52, and then discharged throughanother line 58 to a suitable disposal point. The liquefied gas beingrevaporized is directed to the tubes of the other heat exchanger 54 by aline 60 and discharged from the exchangr 54 as a vapor through line 62leading to any desired point of use. It will be assumed that theliquefied gas passing through the line 60 has been pressurized to thedesired pressure as described in connection with Fig. 1.

The heat transfer medium is in the form of a material which undergoesphase changes during passage through the heat exchangers 52 and 54substantially in the same manner as previously described. The vaporizedheat transfer medium is discharged from the heat exchanger 52 through aline 64 to the inlet of a suitable device 66 forming a work-producingzone. The device 66 is preferably a'turbine, but may be any other formof engine which may be operated by expansion of the vaporized heattransfer medium. The heat transfer medium is reduced in pressure bypassage through the work-producing device 66, and the resulting energymay be recovered in any desired form, such as by rotation of the shaftof a turbine. The heat transfer medium discharging from thework-producing device 66 is still at least mostly in the form of avapor, but at reduced pressure. This reduced pressure heat transfermedium is directed through another line 68 to the heat exchanger 54wherein the heat transfer medium is condensed and the liquefied gas isvaporized by a transfer of heat from the heat transfer medium to theliquefied gas. The major portion of this heat is preferably derived aslatent heat, such that the temperature of the heat transfer medium willnot be sub stantially reduced by passage through the heat exchanger 54.The condensed heat transfer medium is discharged from the heat exchanger54 through a line 70 to a pump 72, whereby the pressure of the condensedheat transfer medium is substantially increased. The pressurized andcondensed heat transfer medium is returned through a line 74 back to theheat exchanger 52.

. The maximum power recovery possible in a cycle as disclosed in Fig. 2and described above, is related to the heat rejection by the heattransfer medium in the heat exchanger 54 and the temperatures of theheat source and the liquefied gas passing through the heat exchanger 54in the following manner:

where:

W=maximum work, B.t.u./hr.

Q =heat rejection, B.t.u./hr. T =temperature of heat source, R. T=temperature of liquefied natural gas, R.

Consider the case of a cycle working between 50 F. and -2.40 F.Substitution in the above formula gives:

It is theoretically possible, therefore, to recover 1.32 B.t.u./hr. ofwork equivalent for each B.t.u./hr. of heat removed in the heatexchanger 54 (the condenser) when working between these temperaturelevels. The actual amount of power recovery will, of course, be less,since the various apparatii do not operate at 100 percent efficiency.However, the power required to operate the pump 72 and provide anincrease in the pressure of the condensed heat transfer medium equal tothe pressure drop through the device 66 is small, compared with thepower recovered through the device 66, such that the net power recoverymay be profitably used to operate auxiliary equipment in a systempracticing the present invention.

In the event a portion of the heat transfer medium condenses in thedevice 66, a superheater 76 may be interposed in the line 64 leadingfrom the heat exchanger 52 to the device 66 as shown in Fig. 3. Thesuperheater 76 may be heated by any suitable means, such as steamcirculated to the superheater through a line 78 and discharged throughline 80.

In the event the temperature of the condensed heat transfer medium getsbelow the freezing temperature of the heat source, or Whenever desired,a portion of the vaporized heat transfer medium may be by-passed topreheat the heat transfer medium entering the heat exchanger 52. Thismay be accomplished by extending a line 82 from line 64 downstream ofthe heat exchanger 52 and upstream of the device 66 back to the line 74downstream from the pump 72, as also illustrated in Fig. 3. However, apump 84 must be interposed in the line 74 downstream of the connectionof the by-pass line 82' to feed the mixed heat transfer medium to theheat exchanger 52.

Where continuous revaporization is required, it is preferred to providea plurality of systems in parallel, such as the three systems generallyindicated by :reference character 86 in Fig. 4. Each of the threesystems 86 may be easily designed to handle 50 percent of the requiredrevaporization capacity, such that one of the systems may be out ofoperation at any one time for inspection and repairs. It will beunderstood that when only two systerns are provided, each system shouldhave a capacity equal to the total revaporization capacity in order thateither of the systems may be taken out of operation for inspection orrepair while the other system continues the revaporization process.

The liquefied natural gas is fed to an installation such as illustratedin Fig. 4, through a line 88 from a suitable liquefied natural gasstorage tank, such as the tank 8 illustrated in Fig. 1 and previouslydescribed. The liquefied natural gas in the line 88 will ordinarilyconsist of a major portion of methane and minor portions of heavierhydrocarbons, such as butane and propane, and will be at aboutatmospheric pressure and at a temperature from 240 to 258 F., dependingupon the composition of the stream. This liquefied natural gas in theline 88 is fed to three separate pumps 90 for increasing the pressure ofthe liquefied natural gas and feeding the liquefied natural gas to aheader 92 communicating with the outlet of each of the pumps 98. It willbe observed that any of the pumps 90 may be isolated, such that theliquefied natural gas from the line 83 will be directed through theremaining pumps 90 to the header 92. It is also desirable to provide aby-pass line 94, at the outlet of each pump 96 to selectively direct aportion of the high pressure liquefied natural gas into a header 96. Thehigh pressure liquefied natural gas in the header 96 may be used toprime any of the pumps 90 when such pumps are being placed in operation.

The high pressure liquefied natural gas in the header 92 is selectivelydirected through feed lines 98, 100 and 102 to the separaterevaporization systems 86. Since the systems 86 are of the same design,it is believed necessary only to describe one in detail, such as thesystem shown at the left end of Fig, 4. The high pressure liquefiednatural gas flowing through the line 98 is directed through the tubes ofa heat exchanger 104 acting as a vaporizer for the natural gas, suchthat the natural gas flowing through the discharge line 1% from the heatexchanger 164 will be substantially in the form of a vapor. The gasdischarged from the heat exchanger 104 is directed into a separator 108for removing condensate from the stream. A portion of the condensatefrom the separator 8 is directed back to the heat exchanger 104- througha line 1111 for reheating thereof. This portion of the condensate in theseparator 1118 may be directed through the heat exchanger 104 by agravity process, such that when the condensate level in the separator108 tends to exceed the liquid level in the exchanger 104, an additionalamount of condensate will be directed back through the exchanger 1% forreheating.

As previously indicated, a liquefied natural gas will ordinarily containat least a minor percentage of heavy ends, such as butane and propane,which will ordinarily collect in the lower portion of the separator 108as a condensate. Therefore, a portion of the condensate from theseparator 108 may be directed into a header 1121eading to a suitablestorage vessel 114 where the heavy ends may be collected and selectivelydischarged through a line 116. It will also be observed that condensatefrom the separators 1118 of the remaining systems is also directed intothe header 112i for storing additional heavy ends in the vessel 11.4.The fiow of condensate into the header 112 from each separator 108 isregulated by a valve 118 in turn controlled by a liquid level controller120 mounted on the respective separator.

The overhead from the separator 108' will be in the form of a vapor andis discharged through a line 122. A flow controller 123 is connected tothe line 122 and a valve 124' in the liquefied gas feed line 98 tocorrelate the feed of liquefied gas with the amount of vapor produced bythe heat exchanger 104. For example, if the composition of the liquefiedgas feed changes, the amount of vapor produced will vary, and thequantity of liquefied gas fed to the respective system must be variedaccordingly to prevent an over or under supply of liquefied gas to theexchanger 104- and separator 1118.

The natural gas revaporized by each of the systems 86 is directed into aheader 126 leading to another separator 12% for removal of anycondensate which may have formed in the lines 122 or the header 126. Thecondensate in the separator 128 is discharged through a line 130 intothe heavy ends storage vessel 114. It will also be noted that the flowthrough the discharge line 130 is controlled by a liquid levelcontroller 132 mounted on a side of the separator 128. The vaporoverhead from the separator 123 is directed through a discharge line 134for use either as a fuel or for use in a subsequent reforming operationin the manner previously described. The natural gas in the line 134 willbe in gaseous form and at an elevated pressure for ease of transporationor subsequent use as a fuel.

The heat exchanger 104 is preferably heated by a closed propane cycle,wherein propane is condensed in the exchanger 104 and then falls bygravity through a line. 136 to a lower'heat exchanger 13?. As before,the condensed propane is revaporized in the heat exchanger 138, suchthat the propane vapors will rise through a line 140 from the heatexchanger 138 back into the heat exchanger 104; The usual heat sourcefor vaporizing the propane in the heat exchanger 138 is in the form ofsea Water constantly available at an inlet line 142. Sea water from theinlet line 142 is pumped through line 144 to the tubes ofthe heatexchanger 138, as well as to the heat-exchangers 138 of the remainingsystems 86. The sea water discharging from the heat exchanger 138 isdirected back through a line 146 to a header 148 for convenient disposalof the used water. The amount of sea water directed throughthe heatexchanger 138 is regulated by a valve 149 which in turn is controlled bythe temperature of the condensed propane through use of a temperaturecontroller 150 con-. nected to line 136, such that the amount of heatavailable. to the heat exchanger 138 may be controlled as desired.

In the event sufiicient sea water is not available, or is not availableat a suificiently high temperature to provide an effective heat sourcefor vaporizing the propane, or whenever desired, a furnace 151 may beused. A furnace 151 is preferably installed for each of the systems 86and is heated by a suitable fuel from a fuel line 152. This fuel may beeasily obtained by bleeding off a portion of. the natural gas in thenatural gas discharge line 134 as illustrated at the right hand end ofthe flow diagram. The condensed propane may be directed from the line136 through a by-pass line 154 for passage through the respectivefurnace 151 where the propane will be revaporized; The propane vaporswill in turn rise through a line 156 which is joined with the previouslydescribedpropane vapor line 140 for flow into the upper heat ex changer1194. The amount of fuel fed to the furnace 151,

and hence the temperature of the furnace 151, is com trolled by a valve158 in turn controlled by the temperature of the condensed propane inthe line 136, in the same manner as the temperature of the exchanger 138was controlled, as previously described.

Although the propane cycle for each of the systems '86 is a separateclosed system, the amount of propane in each system will invariablychange. make-up line 160 is extended 138 to :a propane supply and inturn communicates with a from the heat exchanger discharge line 162,which requires additional propane, the additional be directed throughthe respective line 160 with the propane in the respective system.

hand, excessive propane in discharged through the line On the other Aspreviously noted, the condensate from each of the separators 108 isdirected through the header 112 tothe heavy ends storage vessel 114, andthese heavy ends are in turn discharged through line 116. However, aportion of the condensate in the Therefore, this boil-01f or a line 164into the fuel gas header 152 to combine with fuel supplied to the header152 from the natural gas supply and by use of a cheap and readilyavailableheatI source, without the formation of any solids on the heatTherefore, a propanesuitable propane storage- (not shown). In the eventeither of the propane systems propane mayand combined one of the systemsmay be vessel 114 will vaporize and may be readily used as a fuel forfiring the furnaces 151. overhead is directedthroughr provides a simpleand 9 exchangers used for the revaporization process. Furthermore, thepresent invention provides for a power recovery in a revaporization ofliqueued natural gas, such that the net power required for a system willbe reduced to a minimum.

Changes may be made in the combination and arrangement of steps andprocedures, as well as the various items of equipment and apparatus,heretofore set forth in the specification and shown in the drawings, itbeing understood that changes may be made in the precise embodimentsdisclosed without departing from the spirit and scope of the inventionas defined in the following claims.

I claim:

1. A method of vaporizing a liquefied gas having a boiling temperaturerange below the temperature of a heat source, comprising the steps of:

(a) vaporizing a liquid heat transfer medium with the heat source,

(b) reducing the pressure of the vaporized heat transfer medium in awork-producing Zone,

() condensing the heat transfer medium with the liquefied gas whilesimultaneously vaporizing the liquefied (d) pressurizing the condensedheat transfer medium, and

(e) recycling the heat transfer medium through steps and 2. A method asdefined in claim 1 characterized further in superheating the vaporizedheat transfer medium prior to reducing the pressure thereof in thework-producing zone.

3. A method as defined in claim 1 characterized further in combining aportion of the vaporized heat transfer medium with the pressurized andcondensed heat transfer medium to preheat the heat transfer medium priorto revaporization thereof, and pressurizing the combined vaporized andcondensed heat transfer medium prior to revaporiz-ation thereof.

4. A method as defined in claim 1 characterized further in that the heatsource is sea water.

5. A method as defined in claim 1 characterized further in that heatsource is 6. A method as defined in claim 4 characterized further inthat the heat transfer medium is propane.

7. A method of utilizing heat from a readily available heat source forvaporizing a liquefied gas having a boiling temperature below thefreezing temperature of at least one component of the heat sourcecomprising passing the liquefied gas in heat exchange relationship witha vaporized heat transfer medium having a condensation temperature abovethe boiling point temperature of the liquefied gas and a freezing pointtemperature below the boiling point temperature of the liquefied gas andat a rate to vaporize the liquefied gas and condense the heat transfermedium, passing the condensed heat transfer medium in heat exchangerelationship with the heat source '5. having a temperature above theboiling point temperature of the heat transfer medium and in which nocomponent of the heat source has a freezing point temperature above thetemperature of the heat transfer medium and at a flow rate to vaporizethe heat transfer medium, and repeating the cycle.

8. A method of utilizing heat from a readily available heat source forvaporizing a liquefied gas having a boiling temperature below thefreezing temperature of at least one component of the heat sourcecomprising passing the heat transfer medium in heat exchangerelationship with the liquefied gas and alternately the heat source,said heat transfer medium having a frezmg temperature below the boilingtemperature of the liquefied gas and having a temperature between thetemperature of the heat source and the freezing temperature of anycomponent of the heat source while passing in heat exchange relationshipwith the heat source, passing the vaporized heat transfer medium througha Work producing zone with a reduction in pressure before passagethereof in heat exchange relationship with the liquefied gas,pressurizing the condensed heat transfer medium before passage thereofin heat exchange relationship with the heat source and lay-passing aportion of the heat transfer medium from upstream of the work producingzone to the pressurized and condensed heat transfer medium to preheat toheat transfer medium before passage thereof in heat exchangerelationship with the heat source.

9. A method of utilizing heat from a readily available heat source forvaporizing a liquefied gas having a boiling temperature below thefreezing temperature of at least one component of the heat source,comprising passing a heat transfer medium in heat exchange relation withthe liquefied gas, and, alternately, the heat source, said heat transfermedium having a freezing temperature below the boiling temperature ofthe liquefied gas and having a temperature between the temperature ofthe heat source and the freezing temperature of any component of theheat source while passing in heat exchange relation with the heatsource, and characterized further in that the heat transfer medium is aliquid having a moderate vapor pressure at a temperature between thetemperature of the heat source and the freezing temperature of anycomponent of the heat source for vaporization of the heat transfermedium upon passage in heat exchange relation with the heat source.

References Cited in the file of this patent UNITED STATES PATENTS2,111,618 Erback Mar. 22, 1938 2,484,875 Cooper Oct. 15, 1949 2,495,549Roberts Jan. 24, 1950 2,799,997 Morrison July 23, 1957 FOREIGN PATENTS736,736 France Sept. 26, 1932

